Minor bug fix to properly delete sqlmap temporary files on the database server file system at shutdown.

Minor improvements at ICMPsh tunnel to cleanup properly the dbms at shutdown and avoid checking/writing sys_bineval() UDF as it's a PE and needs to be called by sys_exec() only.
Got rid of useless doubleslash param in delRemoteFile() method.
Major code refactoring to xp_cmdshell.py methods and parent calls.